Let's Build Seedling Flats!

We've touched on the subject of seedling flats, but some of you may be wondering..where do I get seedling flats? We build them of course!

We found a great source of untreated cedar lumber in Creston, so we picked up a car load. We need two sizes of flats, 3" depth and 6" depth. This amount of lumber should be enough for all of our flats for the mini-farm.

The power drill is used to drill pilot holes. Because cedar has a tendency to split, it's a good idea to drill pilot holes for screws and nails. We've used two different wood bits, one that matches the screws and one for the nails. You'll need to choose the correct bit size for the nails and screws you're using. We also use a larger drill bit to counter sink our screws, meaning we drill out a shallow hole that matches the size of our screw heads. Doing this allows the screw to settle in flush, and also helps to minimize splitting the wood.

Full size seedling flats (as described in How To Grow More Vegetables) are made 23" x 14". We like to build them half size at 14"x 13.25". The half flats are much lighter and easier to carry when loaded up with moist soil and plants!

We use screws and wood glue to assemble the frames to make sure they are strong and durable. Remember Pilot holes to avoid splitting the wood!

Next we use the same 14" lengths use in the frame to make the bottom of the flat. In this case we use nails, and again drill pilot holes. We don't use screws or wood glue because the bottom boards will be the first to wear and rot, making placements and repairs easier.

For adequate drainage, be sure to leave a gap between each bottom board.

A completed flat!

All of the plants grown on the mini-farm start their life in a 3" seedling flat. There are times when several dozen flats will be in use at the same time, so we have to build many! Today we built 8 flats, a good start and enough to start all of our onions and leeks.

So why use seedling flats?

It's a combination of resource conservation and efficiency.

Growing seedlings in flats until they are mature means we're keeping our growing beds available for other crops. We're also using a small fraction of the water by having our plants concentrated in flats until mature and ready for transplant.

Let's consider Carrots as an example. We start Carrot seed in a 3" flat, where they grow for 3-4 weeks. When ready, seedlings are transplanted on 3" centers in the growing bed. It takes 6 flats of carrots to fill a 100 square foot bed. We use 1/4 gallon of water per flat per day, or 1.5 gallons per day. If we were to direct sow our carrot seed instead of using flats, we would need 10 gallons per bed per day. If we crunch the numbers, we discover that we're saving 238 gallons of water over a 4 week period by using flats! Maximizing the time our seedlings spend in a flat just makes good sense!

We start more seeds than required in our flats, which allows us to be more selective in which plants make it to the growing bed. Additionally we keep "spares" in our flats in order to replace any seedlings that perish soon after transplant. To achieve maximum yields it's very important we use all of our growing area efficiently at all times!

We also have to consider the sustainability of every aspect of the mini-farm. Traditionally used plastic trays quickly deteriorate and contribute to landfills, and large amounts of energy and oil are used in their manufacturing. Seedling flats are made of a renewable and non-toxic resource, last for many years, and can be repaired over time.

Our research has also shown that seeds sowed together in a flat have a higher and faster rate of germination, and more vigour when compared to seeds grown in individual plastic cells.

Whether you're a backyard gardener or a large CSA, seedling flats will reduce water consumption, reduce your carbon footprint, and decrease the amount of plastic that ends up in the landfill.